Manufacturers of high resiliency polyurethane foam typically use masterbatches consisting of one or more, usually two, polyols plus silicone surfactant, water, amine catalysts and possibly organometallic salts, blowing agent, crosslinkers, dyes or pigments and flame retardants in the manufacture of automotive seating cushions and backs. These are called the "B" side components. Depending on the size of the individual molding plant, the respective masterbatches may be consumed in as short as 2-4 hours or as long as 4-5 days. One of the typically used polyol masterbatches contains an in-situ made polyurea dispersion (PUD). Masterbatches comprising a polyurea dispersion-containing polyol [(PUD) polyol] and utilizing an acid blocked amine catalyst package rapidly change in reactivity when used over several days. Typically after several hours storage, this reactivity drift becomes apparent. Accordingly, very large volume users who consume a masterbatch over a 2-4 hour period never exceed the original initiation period whereas low to moderate volume molders generally will consume their masterbatches over 2-4 days experiencing the cure drift problem.
Stoichiometrically, one isocyanate group is required to react with one active hydrogen group in the polyurethane reaction. In practice, a slight excess of the isocyanate is used to react with water to generate carbon dioxide to expand the mixture into a foam. The ratio of isocyanate to active hydrogen is referred to as the "isocyanate index".
Molders typically run between 95-105 isocyanate index in producing their seating foam holding to a preselected level .+-. one isocyanate index unit. If the index drops significantly below the selected value, the foam is undercured with poor initial and somewhat diminished final physical properties. If the index is greater than about 110, the foam develops a hard "boardy" feel and loses its resiliency. Both results are commercially unacceptable.
When the PUD polyol masterbatch is used, the isocyanate index drops from the selected index value of typically 102.+-.1 to the 80-85 or lower range after 8 hours. In order to maintain uniform production, the polyurethane molders must continuously add more isocyanate to hold the selected index range. This increases the molder's cost to produce commercially acceptable foam.
All polyurethane foamers, regardless of size, require a slight delay of 2-3 seconds in foam initiation to allow the molds to close before the foam rises over the mold part line. Typically, this delay is achieved by using an acid blocked catalyst package.
The PUD polyol supplier recommends to the foam molders that non-acid blocked catalysts be used as a means of ameliorating the PUD polyol masterbatch cure drift. This approach however, causes the molder other problems. If catalyst levels are used to provide a molded foam piece that is sufficiently cured to remove from the mold without tearing or accepting handling marks on the surface, the foam forming reaction is sufficiently advanced at mold closure to have the fresh rising foam flow over the part line. Also, the mold lid typically contains inserts which are driven into the rising foam during closure inducing stresses and shear collapse. The overflow reduces the physical strength of the resulting foam product and wastes material. The shear collapse also reduces the physical properties, quality and durability of the cured foam product.
The alternate procedure of undercatalyzing the B-side produces undercured parts that lack sufficient integrity to be easily removed from the mold without tearing or accepting surface imprints. If the tear is either large enough or in a critical area, the part must be scrapped. If the tear is minor or in a non-critical area, it can be repaired. However, the molder incurs an economic penalty.
U.S. Pat. No. 4,582,861 discloses a method for preparing polyurethane product by the reaction of an organic polyisocyanate with a polyester or polyether polyol in the presence of a catalytically effective amount of a catalyst system consisting essentially of a tertiary amine and 1-35 wt %, based on the tertiary amine, of an N-hydroxyalkyl quaternary ammonium salt.